As demand for energy varies by the time of day and year, continuous supply depends on storage of energy to meet peak requirements in excess of a base energy demand. To level peak usage requirements, gas or liquid hydrocarbons can be stored in large quantities during periods of excess supply, and then released from storage during periods of insufficient supply. Furthermore compressed air may be generated by e.g. wind power, stored in a subterranean salt cavern, and subsequently released and used to generate power with pneumatic motors during periods of high demand and/or during periods when, e.g. wind speeds or output levels of other naturally available power sources are low.
Storing hydrocarbon gas involves compression and/or liquefaction of gas and pumping the compressed and/or liquefied hydrocarbons into large volumetric spaces, while naturally liquid hydrocarbons are simply pumped into said large volumetric spaces.
Embodiments of the present invention relate to the creation and operation of large-volume storage caverns formed in subterranean salt deposits, located on-shore and off-shore, primarily used for the storage of gases and/or liquids, such as hydrocarbons used in the supply of energy.
The present invention relates, generally, to apparatuses, systems and methods usable to create and operate solution mined storage wells. Embodiments of the systems and methods can be used in controlling the formation of the storage wells within salt deposits, controlling and directing the flow of the liquid and/or gas into or out from the wells, and for performing operations, such as batch drilling, completion, solution mining or leaching, dewatering, and below ground gas or liquid storage operations.
Generally, above ground storage costs are greater than below ground storage costs, because the utility of inhabitable above ground space is greater than uninhabitable below ground space.
Thus, conventional methods include below ground mining of a storage facility to create large liquid and gas tight storage spaces for hydrocarbon gas or liquids, known as solution mining, leaching, or leach mining, of subterranean salt deposits.
Leach mining of a subterranean salt deposit involves placing a well bore in the salt deposit and pumping water into the salt deposit to dissolve the salt, then extracting the salt laden brine to create a cavern below ground where gas may be stored.
The density of high quality subterranean salt deposits creates a gas tight barrier for storage of said hydrocarbon gases and liquids, once the entry point into the salt is sealed.
Generally, onshore leach mining of subterranean salt deposits is less resource demanding than offshore leach mining of subterranean salt deposits because facilities must be built above ocean level to facilitate said offshore leach mining. The majority of leach mining operations to-date have therefore occurred onshore using relatively simple construction methods.
Additionally, the limited quantity of onshore high quality subterranean salt deposits close to hydrocarbon gas transmission facilities often limits the number of solution mined onshore storage facilities that may be constructed.
However, there are sometimes high quality salt deposits offshore in proximity to large quantities of hydrocarbon production or transmission facilities, generating utility for constructing offshore gas storage facilities in the form of salt storage gas caverns where no suitable onshore deposits exist.
Unfortunately, the relatively simple technology and methods for construction of onshore gas storage facilities are not cost or resource effective given the high costs and complex logistics of working in a confined space offshore.
Conventional onshore methods and apparatuses for solution mining are particularly unsuitable for offshore applications due to the number of required drilling and/or work-over rig visits to construct a cavern, and due to the high cost of the offshore operations and sea state requirements of moving such ocean going vessels.
As onshore construction methods and apparatuses are impractical and oil industry existing or prior art apparatuses are often unsuitable, no fit-for-purpose existing or prior art offshore construction methods or offshore gas storage cavern apparatuses exist.
Embodiments of the present methods, systems, and apparatuses are capable of withstanding the thermal cycling involved with intermittently compressing and expanding large volumes of gas, storing liquids, dewatering and solution mining to reduce the quantity of resources needed, by simplifying the logistics required for construction of an offshore gas storage cavern with a single flow diverting string usable to perform necessary functions, which would require multiple string installations and removals when using conventional apparatuses, systems and methods.
Generally, practitioners create bore holes into subterranean salt deposits and place conduit segments, such as casing joints, between the subterranean strata and the bore passageway using metallurgical sealing, i.e. welding, to secure each conduit segment or casing joint.
Practitioners in salt cavern well construction often weld the casing joints together to improve the thermal cycling of properties of the conduit or casing string. After placing welded casing strings in the bore hole, practitioners place cement between the subterranean strata and the welded casing string.
An embodiment of the method of the present invention, can include using an existing snap together coupling connection, not presently used in the art of constructing and using storage spaces in salt deposits, to remove the need to weld casing and, thus, save significant time.
Thus, the common practice for creating a series of bore holes emanating from previous casing bores through subterranean strata includes repeating the process of welding and cementing casing, followed by boring until the top of a desired subterranean salt deposit is reached.
Once a bore hole has been urged through the subterranean salt deposit, and a welded casing has been cemented in place above the depth where the solution mined storage space is intended, practitioners in the art of gas cavern wells generally place threaded conduits or casing strings, referred to as leaching strings, within the welded casing string and bore hole, extending downward from the casing through the subterranean salt deposit.
Using conventional methods, the leaching strings are only temporary conduits, requiring fluid pressure integrity during the solution mining process, thus threaded connections are used.
Embodiments of the present invention include a flow diverting string that can be permanently used during solution mining, dewatering, and storage operations to replace these leaching strings, and other strings normally used after removal of the leaching string.
In conventional practice, water is then pumped down these threaded casing strings, which creates dissolved salt or brine by placing water next to the salt deposit, that is returned through the annulus, between the threaded leaching casing strings, in a forward fashion and returned through the inner bore of the internal leaching string in a reverse fashion to improve the rate of salt dissolution.
For additional control and to prevent water from dissolving salt in undesired locations, a blanket comprised of gas, such as nitrogen, or a liquid, such as diesel, is placed through the annulus between the threaded leaching strings and the bore of the well or cavern wall.
Occasionally, the blanket is adjusted and/or the threaded casing is adjusted and/or removed from the well or cavern, and a device, such as sonar, is inserted into the bore to determine if the cavern is being created in the correct shape.
In conventional practice, if the cavern is not leaching as intended or solution mining is to be carried out in stages, the blanket and/or threaded casing are reconfigured one or more times to correct a misshapen cavern or to create space in a stepwise fashion by affecting the dissolution of salt during solution mining.
Using conventional methods, two concentric strings are used for the leaching, and a large hoisting rig is required to remove the inner string (2 of FIG. 1) before the rig can move the outer string (2A of FIG. 1) and re-install the inner string.
The conventional practice of raising the outer (2A of FIG. 1) leaching string is required to adjust the depth at which water is released from between the outer and inner (2 of FIG. 1) leaching strings during the prevalent method of allowing lighter water to float above and force heavier brine into the bore of the inner leaching string, thus increasing the salt saturation of the brine.
The primary convention means for determining when the depth of the inner or outer leaching string should be changed is by measuring the shape and extent of salt dissolution within the bore or cavern using a sonar tool. In instances where low resolution is acceptable, sonar measurements can be taken through the leaching strings; however, if high resolution measurements are required, the leaching strings must be removed before taking sonar measurements.
In conventional practice, threaded leaching string casing can be placed deep within the subterranean salt cavern and sections can be cut and allowed to fall to the bottom of the cavern to adjust the fluid circulation point and to prevent the sucking in of insoluble substances that have fallen to the bottom of the created space, after which leach mining of the subterranean salt deposit continues. The conventional practice of intermittent removal of the threaded casing, checking the cavern shape, cutting the casing, and removal and re-insertion of the threaded casing is logistically complex and expensive for onshore facilities, but even more expensive for offshore facilities.
The conventional process of repeating solution mining operations, measuring the cavern shape and potentially changing the depths of the inner and/or outer leaching strings is continued until the desired cavern volume and shape is created.
In conventional practices, after the gas or liquid storage cavern has been created, the threaded casing string is removed, and a welded casing is installed with a valve tree placed at the surface to control access to the storage cavern.
Conventional practice further includes placing a permanent production packer at the lower end of a welded production casing to be engaged with the final cemented casing above the salt cavern, and sealing the annulus between the production casing and the final cemented casing.
Once the production casing and permanent packer are installed, using conventional methods a dewatering string is installed through the production casing string and associated permanent packer to the lower end of the cavern.
Immediately after solution mining, the created cavern is full of brine. Conventional methods require the installation of a dewatering string through the valve tree, including any subsurface safety valves and the production casing, to the bottom of the cavern to remove the brine by forcing a stored fluid or gas into the cavern to urge the brine to the surface through the dewatering string.
Conventional practice is to force brine from a cavern with the liquid or gases to be stored. This practice is often referred to as dewatering.
During storage operations, compressed gas may be allowed to expand during retrieval, but the cavern must be refilled with water or brine to retrieve stored liquids or gas with insufficient pressure to escape the cavern. When compressed gas is stored within a cavern, a risk of escape exists where liquid stored within the cavern generally lacks the pressure to escape.
Hence, in conventional practice, subsurface safety valves are often installed within the conduits above a gas storage cavern to prevent escape of gas, where the subsurface safety valves are generally not needed in liquid storage caverns.
Where it the conventional practice to leave dewatering strings in liquid storage wells for storage and retrieval purposes, the general practice for gas storage caverns having subsurface safety valves is to remove the dewatering string after brine has been extracted through the dewatering process to allow any associated subsurface safety valves and/or valves of the surface valve tree to close conduits leading to the cavern to prevent the unintended escape of gases.
Removal of a dewatering string from a well and cavern full of compressed gas is a hazardous task, that requires expensive safety precautions to remove the dewatering string from the well and cavern, using a process referred to as stripping or snubbing.
Embodiments of the present invention include a flow diverting string that can be permanently left within the well to dewater during liquid storage operations, with internal portions removed to facilitate use of safety valves in gas storage operations, thus, removing the conventional need to perform hazardous stripping or snubbing operations.
As the diameters of salt caverns are limited by the ability to support the roof of the cavern, large salt cavern storage facilities require many caverns which, using conventional practices, require installing, using and removing a plurality of differing strings to first solution mine and, then, dewater each of the caverns, with gas storage caverns potentially requiring hazardous stripping and/or snubbing operations.
Conventional methods for performing operations on multiple wells within a region require numerous bores and conduits, coupled with associated valve trees, wellheads, and other equipment. Typically, above-ground conduits or above mudline-conduits and related pieces of leaching, production and/or injection equipment are used to communicate with each well. As a result, performing drilling, completion, dewatering, snubbing and other similar operations, within a region having numerous wells, can be extremely costly and time-consuming, as it is often necessary to install above-ground or above-mudline equipment to interact with each well, or alternatively, to erect a large rig, then after use, disassemble, jack down and/or retrieve anchors, and move the large rig to each successive well.
Conventional methods for the solution mining of a cavern within a salt deposit require, at a minimum, the mobilization of a large rig, its erection or installation, its use and its disassembly or disengagement from the well after drilling the well, and again after completing the well, and yet again after dewatering the well before the well can be used for gas or liquid storage operations. Any adjustment of the leaching strings, including removal of the inner leaching string prior to movement of the outer leaching string, requires additional large rig erections, work and disassembly, which further increases the costs and logistical complexity.
Significant hazards and costs exist for performing these same drilling, completions, leaching, dewatering, snubbing and other similar operations numerous times. The hazards and costs increase in harsh environments, such as those beneath the surface of the ocean, arctic regions, or situations in which space is limited, such as when operating from an offshore platform or artificial island. Additionally, the cost of above-ground, or above-mudline, valve trees and related equipment can be economically disadvantageous, and the use of such above-ground or above-mudline equipment can be subject to numerous environmental or other industry regulations that limit access and/or the number of wells, due to significant negative environmental impact.
Where movement, installation, performing work, disassembling and removing a large rig from a well or cavern site is often economically viable onshore during all but the worst weather conditions, the addition of offshore wind, waves and tidal movements can often prevent both the movement and operation of a large offshore rig potentially increasing the costs of constructing gas storage facilities in an offshore environment significantly.
A need exists for systems and methods usable for creating and operating a solution mined storage well, that provides greater efficiency and reduced expense over existing methods by reducing above-ground equipment requirements and reducing or eliminating the need to move, erect, and disassemble drilling and/or hoisting rigs and similar equipment between such operations as the drilling, completion, dewatering, snubbing and storage phases of a storage well or between a plurality of storage wells.
A need exists for systems and methods usable for creating and operating a solution mined storage well that can utilize less expensive and smaller wireline and slickline rigs, and alleviating the need for a plurality of subsequent installations and removals of large equipment that require the use of larger and more expensive hoisting rigs.
A need exists for systems and methods usable for creating and operating solution mined storage wells that can perform numerous operations, including batch drilling, completion, solution mining, dewatering, and gas and liquid storage operations, through a single installation of a string.
A need exists for systems and methods usable for constructing and operating large volumetric solution mined storage wells, within underground or subsea subterranean salt deposits, for lowering storage costs and conserving above ground space.
A need exists for systems and methods usable for constructing subsea or underground large, volumetric solution mined storage wells with great accuracy and control of the formation of the storage cavern.
A need exists for systems and methods usable for operating solution mined storage wells that enable operations, including completion, solution mining, dewatering, and gas and liquid storage operations, to be performed on multiple storage wells through a single main bore.
An object of the present invention is to meet at least some of the above needs, at least in preferred embodiments, and to overcome or alleviate at least some of the above-described problems in the prior art.